This invention relates generally to the field of information storage, and more particularly to a circuit and method for timing amplifier stages of a multi-stage reader amplifier for hard disk drive devices.
Hard disk drives are mass storage devices that include a magnetic storage media, e.g. rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servo circuit, and control circuitry to control the operation of hard disk drive and to properly interface the hard disk drive to a host system or bus. FIG. 1 shows an example of a prior art disk drive mass storage system 10. Disk drive system 10 interfaces with and exchanges data with a host 32 during read and write operations. Disk drive system 10 includes a number of rotating platters 12 mounted on a base 14. The platters 12 are used to store data that is represented as magnetic transitions on the magnetic platters, with each platter 12 coupleable to a head 16 which transfers data to and from a preamplifier 26. The preamp 26 is coupled to a synchronously sampled data (SSD) channel 28 comprising a read channel and a write channel, and a control circuit 30. SSD channel 28 and control circuit 30 are used to process data being read from and written to platters 12, and to control the various operations of disk drive mass storage system 10. Host 32 exchanges digital data with control circuit 30.
Data is stored and retrieved from each side of the magnetic platters 12 by heads 16 which comprise a read head 18 and a write head 20 at the tip thereof. The read 18 and write 20 heads comprise magneto-resistive heads adapted to read or write data from/to platters 12 when current is passed through them. Heads 16 are coupled to preamplifier 26 that serves as an interface between read/write heads 18/20 of disk/head assembly 10 and SSD channel 28. The preamp 26 provides amplification to the waveform data signals as needed. A preamp 26 may comprise a single chip containing a reader amplifier 27, a writer amplifier, fault detection circuitry, and a serial port, for example. Alternatively, the preamp 26 may comprise separate components rather than residing on a single chip.
FIG. 2 shows a reader amplifier 27 of the prior art comprising input amplifier stage 12 coupled in series to middle amplifier stage 14 which is coupled to output amplifier stage 16. The reader amplifier 27 chain of amplifiers 12, 14, 16 is utilized to obtain the desired amount of gain.
A problem with reader amplifiers 27 of the prior art is that at certain transitional times in operation, all amplifiers 12, 14, 16 are turned off and then turned on at once, resulting in an excursion in the output signal 34 as shown in FIG. 3. The excursion may be +/xe2x88x9240 mV or greater, for example. Such transitional times occur for various reasons in a hard disk drive system. In a disk drive system having multiple platters 12 written to and read by multiple heads 16, head 16 communication with reader amplifier 27 is often multiplexed. When heads 16 are changed, an excursion may be seen in the output signal 34. Another excursion generating transitional time is the read head changing from an idle state to a read state. Often, a reader amplifier 27 will operate in an idle mode to save power. Because the internal transistors of amplifiers 12, 14, and 16 are typically bipolar, there is a temporary saturation effect when turning on the transistors of middle stage 14 and output stage 16. When this occurs, it takes a certain amount of time for the FETs to recover and arrive back into a non-saturated state. In this case it results in a 6 xcexcs recovery time. The excursion shown between time t1 and the time t2 reflects the spike in the output signal on the reader amplifier output when the reader amplifier 27 is switched from one head 16 to another, or from idle mode to read mode, for example. Another factor contributing to the excursion is ringing of the voltage supply from each amplifier stage 12, 14, and 16 suddenly simultaneously drawing current from the voltage supply.
What is needed is a circuit and method for eliminating or minimizing excursions in the output signal of a reader amplifier 27.
The present invention achieves technical advantages as a reader amplifier circuit and method with improved recovery time when changing from one mode to another, minimizing the excursion on a reader amplifier output signal. A chain of amplifier stages is turned on in a staggered fashion to avoid saturation of transistors in the second and third stages and reduce ringing on the voltage supply. The last output stage is turned on gradually with an RC circuit, reducing ringing and minimizing the excursion of the output signal.
In one embodiment, disclosed is a method of timing the enabling of amplifier stages of a multi-stage reader amplifier for a hard disk drive system. The reader amplifier includes a first stage, second stage and third stage coupled in series. The first stage is adapted to receive an input signal and the third stage is adapted to generate an output signal. The method includes the steps of powering the first stage, delaying the enabling of the second stage, and delaying the enabling of the third stage, wherein excursions on the third stage output signal are reduced.
Also disclosed is a method of timing the enabling of stages of a multi-stage reader amplifier of a hard disk drive system in a reader amplifier having a first stage, a second stage and a third stage coupled in series. The method includes the steps of powering the first stage, waiting a first predetermined time interval, enabling the second stage, waiting a second predetermined time interval, and enabling the third stage so that excursions of the third stage output signal are reduced.
Further disclosed is a reader amplifier circuit for a hard disk drive system, including a first amplifier stage adapted to receive an input signal and a second amplifier stage coupled to the first amplifier stage. A third amplifier stage is coupled to the second amplifier stage and is adapted to generate an output signal. A logic circuit successively enables the second and third amplifier stages such that excursions of the output signal are reduced.
Advantages of the invention include reducing the recovery time after mode transitions and head switch transitions. Saturation of successive amplifier stage transistors is avoided, reducing excursions in the reader amplifier output signal. Ringing on the voltage supply is minimized by staggering the start-up of the chain of amplifiers of the reader amplifier. An additional feature includes delaying the start of the third output stage with an RC circuit, rather than an abrupt turn on.